1. Field of the Invention
The present invention generally relates to a method for producing PMOS devices, and more particularly to a method for preventing boron segregation and out diffusion for producing PMOS devices.
2. Description of the Prior Art
Continuous expansion of integrated circuit density requires chip area to remain the same or even become smaller in order to reduce circuit unit cost incessantly, and the only solution to this is an endless diminishment of the design rules. Moreover, once devices shrink in size, the degree of shrinkage in gate sizes is even greater than for other design rules, and it is mainly because of the taking of the fact of device efficiency into consideration. The junctions of source/drain regions must be shallow to avoid short channel effect when devices shrink in size. Therefore, boron ions (boron or boron fluoride) with low energy and high dosage must be used, and shallow junctions of PMOS devices are formed by carrying out ion implantation. But thermal diffusion might occur inside the silicon wafer that is caused by the implanted boron ions during a follow-up annealing process. This results in low resistivity source/drain regions and high driving current because the boron ion density closest to the wafer's surface is decreased, furthermore, semiconductor device performance is worsened.